Parasitism is a widespread phenomenon in nature. The number of species of parasitic animals is about 7 % of the total number of animal species. The first scientific definition of the phenomenon of parasitism was given by R. Leucart in 1879. Parasitism is defined as a form of coexistence of organisms of different species, in which one organism (parasite) uses another (host) as a source of food and environment, rule, harming him, but not destroying him. The main directions of development of parasitology of the XXI century. They are the development of biological methods for the prevention of parasitic diseases, the creation of specific prevention, and the development of genetically resistant animals to helminthes. In the future, the development of science will be significantly affected by its four components: biotechnology, bioinformatics, biomathematics and molecular research methods.